Tumbling oil prices are dragging down equity markets in crude-producing emerging markets from Mexico to Russia. Now bearish traders are turning their attention to fragile emerging markets sovereign debt as credit spreads widen.

The iShares J.P. Morgan USD Emerging Markets Bond ETF (NYSEArca: EMB), the largest emerging markets bond ETF by assets, has seen its short interest nearly triple since November 21, reports Boris Korby for Bloomberg.

EMB has lost over $871 million in assets over that period while falling about 2%. After profiting from declines in well-known U.S.-focused high-yield bond ETFs, such as the SPDR Barclays High Yield Bond ETF (NYSEArca: JNK) and the iShares iBoxx $ High Yield Corporate Bond ETF (NYSEArca: HYG), in 2014, short sellers have turned their attention to emerging markets debt this year as oil prices have continued sliding, according to Bloomberg.

The $4.1 billion EMB features exposure to 28 countries and about 15% of the ETF’s combined weight is devoted to debut issued by Mexico, Brazil and Russia. Of the major non-OPEC oil-producing nations, no country is more dependent on oil revenue as a percentage of government receipts than Russia. Mexico is second on that list. [Oil Hits Frontier ETFs]

While ratings do not see cause for concern in Mexico amid falling oil prices, Russia is an entirely different story. Production there has reached post-Soviet era highs even as oil futures reside at their lowest levels since April 2009.

Last Friday, Moody’s Investors Service lowered its rating on Russian sovereign debt to one notch to Baa3 from Baa2. The Baa3 rating is the lowest investment grade on the Moody’s scale. Earlier this month, Fitch Ratings lowered Russia’s sovereign credit rating to BBB-, the lowest investment grade, with a negative outlook. [Fitch Downgrade Stings Russia ETFs]

On Dec. 23, Standard & Poor’s placed Russia’s sovereign debt on CreditWatch with negative implications, indicating Russia could lost its already tenuous grasp on its investment-grade credit rating. In April 2014, Standard & Poor’s lowered its rating on Russian sovereign debt to BBB-, the lowest investment grade. It was the first time the ratings agency has downgraded Russia since 2008. [Russia ETFs Fall After S&P Downgrade]